The present invention relates to a method and device for recognizing a trailer or semitrailer of a motor vehicle.
In the case of passenger or utility motor vehicles, for example, certain information regarding trailers or semitrailers, that may possibly be coupled to the tow car or motor vehicle, are needed for electronic stabilization programs (ESP). The essential piece of information in this case is whether or not a trailer is coupled on at all. Such information, for example, is advantageously applied also for brake control, particularly for an ABS/ASR control or a transmission control system. In ESP systems the information on whether a trailer or semitrailer is present may be used for determining a control strategy. That is, in the case where no trailer or semitrailer is present, an ordinary automatic control or regulation strategy is executed. If a trailer or semitrailer is present, then in certain driving situations, in this case, for instance, when there is danger of bending in at low speeds, a regulation strategy deviating from the usual, i.e. a modified regulation strategy is executed, with which the vehicle combination can be stabilized in this driving situation. With this strategy, the stabilizing interventions are mostly carried out in the form of braking interventions on the trailer or semitrailer. An appropriate procedure is also provided for ABS systems (regulation of brake slippage) or ASR (regulation of traction). That means, for the case where a trailer or semitrailer is coupled to the tow car, a modified regulation strategy is carried out. In this case, for example, it is all about functions for avoiding bending in, with which the rear axle of the tow car is possibly regulated to have less slippage.
Trailer recognition devices are known, in which the resistance of a brake or blinking light of the trailer is measured against ground. In doing that, however, the concerned lead to the trailer has, to be cut off, so as not to measure simultaneously the resistance of a brake or blinking light of the motor vehicle as well.
German Patent Application No. 26 40 355 describes a control arrangement for tow cars of vehicle sets, in which at least the tow car is provided with an anti-lock control system. Here, the tow car is designed with a supply line and a plug device, the plug device having a counterpart on the trailer side. A brake light installation of the trailer is connected to the counterpart of the plug. When the brake is operated, if a trailer is attached, a current flows in the brake light installation of the trailer, and at a current measuring device in the supply line a voltage is released which produces a binary switching signal. On the basis of this binary voltage signal the presence or absence of a trailer can be determined.
German Patent No. 44 17 301 describes using a locking relay in the framework of a recognition device for trailer towing. Here, the relay responds when an electric circuit is generated at the plug box leading to the trailer. In practice, preparing such a relay proves relatively costly.
Finally, German Patent No. 39 27 562 describes a device for trailer recognition in trailer trains, whose tow vehicle is fitted with an anti-lock device. This device is used to signal to the driver whether the trailer vehicle also has an anti-lock device, and whether its cable coupling has been done in orderly fashion. For this purpose, the device has an electronic, logical circuit arrangement in which at least one first and one second signal is processed. The system described in this document is considered relatively costly.
An object of the present invention is to provide recognition of a trailer of a motor vehicle that is as simple and low-cost as possible.
According to the present invention, the information as to whether a trailer is coupled to a tow vehicle or not can be prepared in simple fashion. Operating the brake light of the trailer independently of the driver, for instance, can be done using a central control device, especially a control device of an electronic braking system. To do this, no additional sensor mechanism in or at the trailer or semitrailer is required, compared to conventional systems. Furthermore, in the control device, additional electromagnetic components, for example relays, can be avoided, which, particularly with regard to their production and lifetime, can lead to problems in practice.
It is preferred that recognition of a trailer or semitrailer, according to the present invention, be carried out during the starting procedure of the motor vehicle and/or cyclically. Since the condition of trailer coupling will, as a rule, change only during stillstand, the first named measure guarantees that the desired signal will be available immediately after starting. However, for certain applications a cyclical application of the method can prove suitable.
Lighting the brake light of the trailer suitably takes place over a predetermined time interval, in particular 50 msec. By such a brief current application to the brake light it can be avoided that other traffic participants receive false information from longer current application and the resulting longer shining of the brake light, and that the other traffic participants become irritated, since the shining of the brake light is perceived only during longer current application.
It is preferred that the current measured within the framework of the method according to the present invention be compared to a threshold value, and that the determination of the presence or absence of a trailer be made on the basis of a comparison of the measured current with the threshold value. Using this measure makes available an especially simple and numerically low-effort execution of the method according to the present invention.
Expediently, a signal pointing up the presence or absence of a trailer is made available to a control device and/or to the driver of the motor vehicle. For example, such a signal, transmitted to the driver, can be provided as an optical or an acoustic signal.